Examples of conventional solid-fuel-fired boilers include a pulverized-coal-fired boiler that combusts pulverized coal (coal) as solid fuel, for example. Examples of this pulverized-coal-fired boiler include two types of known combustion systems, i.e., a tangential firing boiler and a wall firing boiler.
Of those boilers, in the tangential firing boiler that combusts pulverized coal, secondary-air injection ports for injecting secondary air are disposed above and below primary air injected from a coal-fired burner (solid-fuel-fired burner) together with pulverized coal, serving as fuel, so as to perform airflow adjustment of secondary air around the coal-fired boiler (see Patent Literature 1, for example).
The amount of the above-described primary air needs to be sufficient to convey the pulverized coal, serving as fuel, and therefore, the amount thereof is specified in a roller mill for pulverizing coal to generate pulverized coal.
The above-described secondary air is blown at an amount required to form the entire flame in the tangential firing boiler. Therefore, the amount of secondary air for the tangential firing boiler is generally obtained by subtracting the amount of primary air from the total amount of air required for combustion of the pulverized coal.
On the other hand, in a burner of a wall firing boiler, it has been proposed that secondary air and tertiary air are introduced at an outer side of primary air (for supplying pulverized coal) to perform fine tuning of the amount of introduced air (see Patent Literature 2, for example).